linux-kernel - Re: [PATCH] Revert "scsi: sd: Do not repeat the starting disk message"

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Message-ID: <ZpeIOsEbBIho9P_1@hovoldconsulting.com>
Date: Wed, 17 Jul 2024 11:00:42 +0200
From: Johan Hovold <johan@...nel.org>
To: Damien Le Moal <dlemoal@...nel.org>
Cc: Johan Hovold <johan+linaro@...nel.org>,
	"James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Bart Van Assche <bvanassche@....org>, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] Revert "scsi: sd: Do not repeat the starting disk
 message"

On Wed, Jul 17, 2024 at 07:48:26AM +0900, Damien Le Moal wrote:
> On 7/17/24 01:11, Johan Hovold wrote:
> > This reverts commit 7a6bbc2829d4ab592c7e440a6f6f5deb3cd95db4.
> > 
> > The offending commit tried to suppress a double "Starting disk" message
> > for some drivers, but instead started spamming the log with bogus
> > messages every five seconds:
> > 
> > 	[  311.798956] sd 0:0:0:0: [sda] Starting disk
> > 	[  316.919103] sd 0:0:0:0: [sda] Starting disk
> > 	[  322.040775] sd 0:0:0:0: [sda] Starting disk
> > 	[  327.161140] sd 0:0:0:0: [sda] Starting disk
> > 	[  332.281352] sd 0:0:0:0: [sda] Starting disk
> > 	[  337.401878] sd 0:0:0:0: [sda] Starting disk
> > 	[  342.521527] sd 0:0:0:0: [sda] Starting disk
> > 	[  345.850401] sd 0:0:0:0: [sda] Starting disk
> > 	[  350.967132] sd 0:0:0:0: [sda] Starting disk
> > 	[  356.090454] sd 0:0:0:0: [sda] Starting disk
> > 	...
> > 
> > on machines that do not actually stop the disk on runtime suspend (e.g.
> > the Qualcomm sc8280xp CRD with UFS).
> 
> This is odd. If the disk is not being being suspended, why does the platform
> even enable runtime PM for it ? 

This is clearly intended to be supported as sd_do_start_stop() returns
false and that prevents sd_start_stop_device() from being called on
resume (and similarly on suspend which is why there are no matching
stopping disk messages above):

	[   32.822189] sd 0:0:0:0: sd_resume_common - runtime = 1, sd_do_start_stop = 0, manage_runtime_start_stop = 0

> Are you sure about this ? Or is it simply that
> the runtime pm timer is set to a very low interval ?

I haven't tried to determine why runtime pm is used this way, but your
patch is clearly broken as it prints a message about starting the disk
even when sd_do_start_stop() returns false.

> It almost sound like what we need to do here is suppress this message for the
> runtime resume case, so something like:

No, that would only make things worse as I assume you'd have a stopped
disk message without a matching start message for driver that do end up
stopping the disk here.

> However, I would like to make sure that this platform is not calling
> sd_resume_runtime() for nothing every 5s. If that is the case, then there is a
> more fundamental problem here and reverting this patch is only hiding that.

This is with the Qualcomm UFS driver, but it seems it just relies on the
generic ufshcd_pltfrm_init() implementation.

Also not sure why anyone would want to see these messages on every
runtime suspend (for drivers that end up taking this path), but that's a
separate discussion.

Johan